Turbidity Meter – TurbSense®

Sapphire is used for the windows as it is tough and scratch resistant (much more than glass or quartz). Its use also allows the windows to be thin (because it’s stronger) and therefore have good optical transmission.

The maximum temperature of the sample being monitored is 50°C. We choose 50°C because it is well within the upper limits of the electronic components that we use and still gives a good range or temperature for measuring online turbidity.

You can if the turbidity is high enough or the pipe is big enough.

To achieve a high level of performance the TurbSense^® uses a powerful light source and sensitive optics. This means that in a pipe, reflections from walls and bends can cause inaccurate readings. The higher the turbidity, the closer the reflective surfaces can be so that at >200NTU putting the TurbSense^® online turbidity meter in a pipe should be no problem.

For optimum performance fit an AutoClean unit to the sensor. This can be used to periodically clean the sensor window to ensure the highest accuracy in readings. Try to avoid placing the sensor in direct sunlight as the sensitive optics can pick up infra-red light emitted by the sun.

The flow chamber removes entrained bubbles to prevent them causing an interference to measurements. Its black polypropylene construction eliminates stray light and the lid removes ambient light, both potential sources of interference in measurements.

Turbidity is a measure of the cloudiness of water. How we measure turbidity is defined in international standard ISO 7027 and several US EPA standards. It is a measure of the amount of light that is scattered at 90 degrees. The more light that is scattered the higher the turbidity.

There are several units that are used for turbidity measurement and all of them are determined by the amount of light that is scattered through 90 degrees by a defined solution of formazin in water. The most common unit is NTU (Nephelometric Turbidity Unit) but there are also other units such as FTU (Formazin Turbidity Unit) and FNU (Formazin Nephelometric Unit). Typically NTU is used when the method is in compliance with a US EPA method such as 180.1 and FNU is used when the method of measurement is in compliance with the ISO standard 7027, but these are not fixed rules and the three units can be used interchangeably.

There is a hard upper limit for the measurement of turbidity which is 4000 NTU. This is the top of the definition of turbidity. Typically turbidities that people measure are much lower, for example drinking water will be less than one NTU and ofter less than 0.1 NTU. River water is typicall below 10 NTU when it is “clear” but can go up to 1000 NTU when it looks “muddy”.

1 NTU (Nephelometric Turbidity Unit) is a measure of the cloudiness of water that equates to a particular amount of Formazin dissolved in water. 1 NTU water looks clear to the human eye and might be found in a swimming pool or in drinking water.

When a turbidimeter (whatever the geometry between the source and the detector) is calibrated against Formazin it has the units FTU (Formazin Turbidity Unit). If the device complies with the US EPA mandated geometry and light source then the unit becomes NTU (Nephlometetric Turbidity Unit). If the device complies with the International standard ISO 7027 then the unit is FNU (Formazin Nepholmeteric Unit), although it is more commonly referred to as NTU. The relationship between FTU:NTU:FNU is 1:1:1.

Every TurbSense^® is factory calibrated and is supplied with a calibration sheet (Certificate of Calibration).

The TurbSense^® turbidimeter uses Modbus to communicate with the control electronics, that means that the sensor cable can be extended or shortened, but it cannot be replaced. This is because it is potted into the sensor to prevent water leaks.